In recent years, commercial and sport fishery resources have declined considerably and various conservation measures are now practiced in an attempt to slow down the decline. One such measure is the release of fish after capture. More often, those fish species caught principally for sport are released, but those valued as food are also sometimes released when the catch is excessive. In any event, releasing fish, hopefully unharmed, has become a common conservation practice in many of the sport fisheries.
Obviously, it is preferable to remove the hook from captured fish before they are released, and the smaller inshore fishes can be easily netted when captured to facilitate hook removal. However, the larger oceanic fishes generally cannot be netted, and hook removal is therefore more difficult. Gaffing or otherwise bringing such fish aboard for hook removal is often too stressful and many such fish die soon after being released. Therefore in the oceanic big game fisheries it has become the preferred practice to cut loose the fishing line or leader when the fish is close alongside the boat, leaving the hook embedded in the fish.
In addition to the deliberate and purposeful release of fishes with embedded hooks, there is also the problem of inadvertent line breakage while fishing. The added burden of a length of fishing line attached to the embedded hook presumably further reduces the fish's chances of survival. In sport fisheries, it is commonly the objective to catch ever larger fish with the lowest possible test line, and this form of competitive fishing has also contributed to the overall problem.
In any event, it is now known that an embedded hook in a free swimming fish can take many months to disintegrate, depending on the steel composition and the protective plating. Meanwhile, possible adverse effects of the embedded hook with its attached remnant of line or leader could include impairment of feeding behavior and/or ulceration or infection of the hook wound. It seems likely that these cumulative effects significantly reduce the chances of survival of released fish.
Because seawater is an excellent electrolyte, severe corrosion can occur when two different metals are coupled together underwater. One metal in the couple will be anodic to the other and the degree of corrosion depends partly on the relative position of the two metals in the galvanic series for seawater. Usually, the farther apart in the series (i.e., the greater the difference in potential) the greater will be the acceleration of the corrosion rate of the anodic member of the couple. A carbon steel fish hook is anodic when coupled to a less active (cathodic) metal such as nickel, silver, or gold. The corrosion rate is controlled by the nobility of the cathode metal and on the ratio between the cathodic and anodic surface areas exposed to sea water. A smaller anodic (steel) area coupled to a larger cathodic (e.g., gold) area immersed in seawater will result in a greatly increased rate of corrosion attack on the anode. Conversely, a small cathode area coupled to a large anode area will have only a minor influence on the rate of corrosion.